Recently, hybrid media have been put into practical use. Each of the hybrid media includes a non-rewritable area, which becomes not-rewritable once data is written in it, and a rewritable area, which is rewritable. Such hybrid media are disclosed by PATENT DOCUMENT 1.
One possible use of the hybrid media is that a distributor prerecords a content such as music, movies and games in the non-rewritable area, distributes the media, and then distributes, via a network and so on, an additional content which is to be added into the rewritable area.
For instance, the distributor can distribute the hybrid media including a movie content to the users, and then distribute, via a network, the making of the movie to the users, as the additional content which is to be added into the rewritable area. In this way, the users can further enjoy the content recorded in the non-rewritable area with the additional content.
However, once the distributor has written a content into the non-rewritable area and has distributed the hybrid media, anybody can write any data into the rewritable area. Therefore, an additional content that is not expected by the distributor might be recorded in the rewritable area and reproduced. Content distributors have demands that the distributed hybrid media be protected against such rewriting, and reproduction of an unexpected and unauthorized additional content.
Patent Document 1
Japanese laid-open patent publication No. 7-235095